The present invention relates to a process to remove certain organically bound metal ions from crude oil.
Basic metals such as calcium, when present in crudes can lead to fouling of heaters and heat exchangers and poison catalysts used in crude processing. When present as inorganic salts, e.g., chlorides, usually in an oil-encapsulated water phase, the salts can hydrolyze to release corrosive mineral acids. Such salts are customarily removed by refinery desalters. However, oil-soluble metal salts such as naphthenates are not removed by conventional desalting. Therefore, oil-soluble, basic metal-rich crudes are less valuable than crudes with low levels of such metals. A process for metal ion removal enables the increase of the value of such crudes.
Hung et al. used fixed bed catalysts in the presence of hydrogen to remove oil-soluble calcium from hydrocarbon feeds (U.S. Pat. Nos. 4,741,821, 4,830,736, 5,102,852). Reynolds et al. removed calcium and/or iron from hydrocarbon feeds to an aqueous phase using aqueous acid and/or salt solutions of hydroxycarboxylic acids (U.S. Pat. No. 4,778,589), aminocarboxylic acids (U.S. Pat. Nos. 4,778,590; 4,778,592), carbonic acid (U.S. Pat. No. 4,778,591), dibasic carboxylic acids (U.S. Pat. No. 4,853,109), and monobasic carboxylic acids (U.S. Pat. No. 4,988,433). These chemical treatments all required pH adjustment to greater than 2, preferably between 5-9 along with a commercial demulsifier in order to overcome the problem of emulsion formation. In another approach, Eckerman et al. (Chem. Eng. Technol. (1990), 13(4), 258-64) and Funk (Am. Chem. Soc. Div. Fuel Chem., (1985) 30(3), 148, 148a, 149, 149a, 150-3) reported on the use of supercritical CO.sub.2 fluid to deasphaltene heavy oils accompanied by some removal of only porphyrin metals (Ni, V) associated with the asphaltenes. As known to those skilled in the art, supercritical CO.sub.2 has different properties and different separation selectivity from aqueous CO.sub.2. Finally, in the pending application (U.S. Ser. No. 961,816, WO 98 14534, published Apr. 9, 1998), oil-soluble calcium removal was effected with CO.sub.2 where no water was added. This treatment maintains one liquid (oil) phase and results in the formation of solid CaCO.sub.3 enabling separation from the oil phase.
It would be desirable to develop a process for removing oil-soluble metals such as calcium that addresses and overcomes the problem of emulsion formation without the need to add demulsifier agents and agents to maintain the pH of the solution. Applicants' invention addresses these needs.